Image stitching has been gaining prominence in many application areas including, for example, computer vision, digital maps, satellite imaging, medical imaging, and even amateur photography. For example, to create an immersive virtual-reality experience, multiple cameras may be used to capture source images covering different parts of a scene. These source images are then “stitched,” that is, joined together, to form a 360-degree panorama that can be used in applications such as interactive panoramic movies, architectural walk-through, multi-node movies, and other applications associated with generating a virtual 3D environment using images acquired from the real world.
Because the source images used for panorama stitching may be generated by different imaging devices, at different times, and/or under different illumination conditions, a well-known challenge for panorama stitching is inconsistency in image parameters of the source images. To solve this issue, the conventional method adjusts the contrasts of two adjacent source images, pair by pair, to ensure that the luminance and/or color histograms in the overlapping regions are matched. This method usually achieves local consistency but not global consistency, due to accumulated error. For example, when more than two source images are stitched using this method, the last stitched source image and the first source image may still have significantly inconsistent luminance/chrominance. Such result may be acceptable in some applications. e.g., mobile-phone applications, where the generated panoramic image often has a larger than normal viewing angle, but less than 360 degrees. However, to generate high-quality panorama and/or 360-degree panorama (i.e., the views shown by the first and last source images actually overlap), it is desirable for the first and last source images to have consistent luminance and chrominance. Therefore, a global luminance/chrominance adjustment method is needed.
The disclosed methods and systems address one or more of the problems listed above.